Process and apparatus for machining by electro erosion

ABSTRACT

A process and installation for machining by electro-erosion, comprising means for measuring the rate of variation of the voltage of the machining gap during the establishment of each discharge, these means acting upon the electrical and/or the mechanical control of the installation.

United States Patent [191 Marendaz June 12, 1973 PROCESS AND APPARATUSFOR MACHINING BY ELECTRO-EROSION [75] Inventor: Georges-Andre Marendaz,Geneva,

Switzerland [73] Assignee': Ateliers Des Charmilles S.A.,

Geneva, Switzerland [22] Filed: Mar. 22, 1972 [2]] Appl. No.: 236,827

[30] Foreign Application Priority Data Mar. 25, 1971 Switzerland 4401/71Mar. 25, 1971 Switzerland 4402/71 [52] US. Cl. 219/69 C, 219/69 G,219/69 M [51] Int. Cl B23p 1/08, 823p 1/14 [58] Field of Search 219/69C, 69 G, 69 M,

[56] References Cited UNITED STATES PATENTS 3,632,942 l/l972 Kondo219/69 C Primary ExaminerR. F. Staubly Attorney-Robert C. Hauke, Ernestl. Gifford and Claude A Patalidis et al.

[57] ABSTRACT A process and installation for machining byelectroerosion, comprising means for measuring the rate of variation ofthe voltage of the machining gap during the establishment of eachdischarge, these means acting upon the electrical and/or the mechanicalcontrol of the installation.

15 Claims, 17 Drawing Figures PAIENIEB 2W5 3.739.137

saw u or 8 PROCESS AND APPARATUS FOR MACHINING BY ELECTRO-EROSION Theinvention relates to a process for machining by electro-erosion,according to which a succession of voltage pulses are applied within themachining gap comprised between an electrode-part to be machined and anelectrode-tool intended to trigger the erosive discharge through amachining fluid filling this gap, the discharges being sustained bycontrolled current pulses, and in which at least one of the followingmachining parameters is automatically controlled:

first, the characteristic values of said electric voltage and/or currentpulses;

second, the physical or chemical conditions of the machining fluidfilling the said gap;

third, the spacing of said electrodes, by means of electric signalsobtained from the voltage measured between the electrodes and/or thecurrent flowing through the latter and/or from a combination of thesesignals.

Generally, the control of the machining conditions is effected bymeasuring the voltage between the electrode and the workpiece, and whenthis voltage reaches a very low value, due to a short-circuit, theelectrode is withdrawn by means of a servo-mechanism, to eliminate theshort-circuit. However, it has been noticed that this procedure is notsatisfactory to obtain good machining results and to prevent defects ofthe machined part and/or damages to the electrode due to partial fusionresulting from electric arcing.

The object of the present invention is to provide a more accuratecontrol of the machining conditions, and consequently to improve theperformances of spark machining equipment. The process according to theinvention consists in detecting the decrease of said voltage, the rateof which is lower than a predetermined value during the establishment ofthe current pulses, and to act on at least one of the machiningparameters, in function of the received electric signal responding tothe presence of a voltage decrease for which the rate is lower than saidpredetermined value.

The enclosed drawings show, diagrammatically and by way of example, oneembodiment of the process according to the invention.

In said drawings:

FIG. 1 is a general view of a very schematic embodiment of theinvention;

FIG. 1A shows a more detailed circuit of FIG. 1;

FIG. 2 illustrates the functioning principle of an electric circuit ofthe machine according to FIG. 1;

FIG. 2A is a block diagram of the generalized type of a control unit;

FIG. 3 shows a part of the circuit according to FIG.

FIGS. 4 to 9 illustrate the diagram of the control units designated IVto IX in FIG. 2;

FIG. 10 shows the command circuit of the servomechanism;

FIG. 11 represents a diagram for the setting of the time intervalbetween two successive pulses;

FIG. 12 is a block diagram of the circuit controlling the rate of flowof the machining fluid;

FIGS. 13 and 14 are illustrating in detail two portions of the circuitillustrated in FIG. 1A;

FIG. 15 shows a diagram permitting the automatic control of the durationof each discharge.

The machine illustrated in FIG. 1 comprises a table 1, forming acontainer, supporting the workpiece 2 to be machined. An electrode 3 isdisplaceable in the direction of the workpiece 2 by means of aservomechanism 4.

The machining current is supplied by a pulse generator 5 which consistsessentially of one or several continuous current sources 6 andelectronic relay 7 connected to the part 2 and the electrode 3 by theconductors 8 and 9 respectively.

The machine comprises also a container 10 for the machining fluid which,usually, is a dielectric liquid. This fluid is drawn in by a pump P andchannelled by a conduit 1 1, controlled by a valve 12, to be dischargedto the electrode 3. The latter is usually equipped with one or severalconduits channelling the machining fluid to its extremity to dischargeit directly in the machining gap.

The machine comprises also a control device 13 acting on the pulsegenerator 5 through a symbolically represented control line 14. Thecontrol device 13 has also an output 15 for the control of theservomechanism 4 assuming the displacement of the electrode and an exit16 which controls the valve 12, controlling the flow of the machiningfluid. This control device 13 has also two inputs 17 and 17a connectedto the piece to be machined and to the electrode, and inputs l8 and 18aconnected to a current measuring shunt S, in order to feed the devicewith the voltage and current in the area of machining or gap.

FIG. 1A illustrates a circuit similar to the circuit of FIG. 1, butfurther implemented, particularly with re spect to the generator 5 and amultiplicity of connections 14a through 14f, allowing action of thecontrol device 13 on the generator 5. The latter is of the typedescribed in the US. application Ser. No. 18,803.

This generator comprises a first monostable multivibrator 5a controllinga second monostable multivibrator 5b, the exit of which is acting on apulsator 36 which is constituted of a switch controlling the basecurrent of a transistor T controlling the current supplied by acontinuous source 6a to the machining gap comprised between theelectrode 3 and the workpiece 2. The duration of the instability periodof the multivibrator 5a is determined through the multivibrator 5b,during which period of time the transistor T is conductive. The durationof the period of time during which this transistor is non-conductive isdetermined by the monostable multivibrator 5b. As shown, the exit of themultivibrator 5b is connected by a line 19a to a commutator 19controlling the inlet of the multivibrator 5a. In this way, when themultivibrator 5b flips at the end of the non-conductive period of thetransistor T a pulse is applied through line 19a and the commutator 19at the inlet of the multivibrator 5a to set it in its unstable positionwhich determines the duration of the pulse for the following machiningsequence.

At will, the commutator 19 allows also to connect the entrance of themultivibrator 5a to a device 5c detecting a current flow between thepart 2 and the electrode 3, by detecting whether the voltage between 17and 17a is lower than the voltage of the source 6a by a value exceedingthe predetermined value, this potential difference resulting from thecurrent flowing through the resistor R Under certain machiningconditions, a time delay occurs between the application of the machiningvoltage between the electrode and the workpiece, and the establishmentof a current discharge between these parts. This time delay is uncertainand can vary greatly from one pulse to the next.

When the detecting device 5c is in operation, the multivibrator 5a isbrought in its unstable position only at the instant that the machiningcurrent is established by a discharge between the electrode and theworkpiece. In this manner, the multivibrator 5a defines the duration ofthe machining current for each pulse, so that all pulses have sensiblythe same energy level and the same duration, independently of theduration of the delay.

The generator 5 comprises also a transistor T as part of the electronicrelay 7 controlling the flow of the machining current. A transistor T aspart of the electronic relay 7a facilitates the establishment of themachining current for each discharge, by applying a high voltage pulseto the gap. To this effect, the transistor T connects the electrode 3 toa source of voltage 612 through a resistor R The application of the highvoltage facilitating the establishment of the discharges originateswithin the control device 13 and follows a line 14a terminating at agate ET of the AND type which renders the transistor T conductive whenit receives simultaneous signals from line 14a and from the pulsator 36.

Transistors T and T are connected each to electrode 3 through a resistorR R respectively, in series with a diode D D respectively. These diodesare protecting the transistors T and T from return electric spikesoriginating at the source 6b during the period in which the transistor Tis conductive.

The transistor T is connected in parallel with the transistor T and iscontrolled by an AND gate, designated by ET intended to increase themachining current whenever the machining conditions are favorable. Tothis effect, a signal is supplied by the control device 13 through line1412, this circuit opening the gate ET to allow the passage of thepulses supplied by the pulsator 36. In this way, the two transistors Tand T are operating in synchronism whenever the machining conditionspermit. Obviously, the transistor T could be replaced by a multiplicityof transistors to further increase the current, when the machiningconditions warrant it.

The control device has two inlets connected to lines 19a and 19b to bemonitored by the beginning of the closing of the transistor T or by thedischarge within the machining gap respectively.

The control device 13 has also the outlets 140 through 14f. The outlet140 is provided for acting upon the duration of the pulses from themultivibrator 5a, as will be further explained with reference to FIG.15.

The outlet 14d is allowing action on the time interval betweensuccessive pulses, as will be further explained with reference to FIG.11.

The outlet 140 allows momentary interruption of the discharges by actionon the pulsator 36, as will be further explained with reference to FIG.3.

The outlet l4finsures a definitive cut-off of the machine by action on arelay 35, in the event that the normal machining conditions can not bemaintained.

The control device 13 is equipped with four pilot lights 31 through 34intended to signal visually any malfunction of the machining process.

Further details of the control device 13 are illustrated in FIG. 2. Itcomprises watching units IV through IX to check the various machiningconditions criterias. The input signals of these control units arechannelled through lines 17 and 17a to convey the voltage between theelectrode and the part to be machined, through lines 18 and 18a for thecontrol of the machining current flow, and through lines 19a, 19brespectively for the synchronization with the beginning of theapplication of a machining tension and with the beginning of theestablishment of each machining discharge respectively.

The watching unit IV detects the presence of abrupt variations ofvoltage between the electrode and the part to be machined, during thedischarges.

The watching unit V checks the presence of voltage variations betweenthe electrode and the workpiece, between one discharge and another. Theexistence of such variations is a criteria of adequate functioning ofthe installation, since it indicates that the machining sparks areproduced successively at different points of the surface to be machined.When on the other hand, several successive discharges are produced atthe same geometrical point of the machined surface, the level of thevoltage does not vary appreciably during the various discharges, and thewatching unit V generates then an output signal indicative ofunfavorable machining conditions. In fact, when the successivedischarges are confined to a particular point of the part to be machinedand of the electrode, localized heat is generated capable of causingdamage to the surface to be machined, prior to the appearance of ashort-circuit.

The watching unit VI is intended to check the pollution level of themachining fluid. This unit in fact checks the decreasing rate of thevoltage between the electrode-tool and the electrode-part during theestablishment of the current pulses. When the pollution level of thefluid is too high, the dielectric fluid becomes sufficiently conductiveto prevent the formation of a machining spark. Then, one simply noticesthe passage of the current pulses between the electrode and theworkpiece, the duration of which is equal to the voltage pulses appliedto the electrode, and the speed of establishing the current is lowerthan when operating with unpolluted fluid.

The watching unit VII is intended to detect a shortcircuit and can beimplemented very simply. In fact, it is sufficient that it reacts whenthe potential between the electrode and the workpiece falls below thepreestablished value during the passage of the current discharge.

The watching unit VIII is intended to check the potential of theelectrodes during the time elapsed from the application of each voltagepulse, between the electrode and the part to be machined, to theappearance of the current flash between the parts.

The watching unit IX checks the performing of the relay 7.

The watching units IV through IX are connected to a circuit 20 by thelines 21 through 29, feeding this circuit with data relating to thepresence or to the absence of the various conditions detected by saidunits. Part of the logic of this circuit 20 channels the data accordingto its nature, on one or the other of the four pilot lights 31 through34. The lighting of each specific light indicates the following relateddefect:

The light 31 indicates an insufficient rate of abrupt variations or theabsence of variations.

The light 32 lights up when the pollution level of the fluid is toohigh.

The light 33 indicates the presence of a short-circuit.

The light 34 indicates a malfunction of the relay 7.

The logic part of the circuit is further provided with two outlets 14cand 14f ending at the current cutoff devices 36 and 35 respectively. Thedevice 35 controls a definitive cut-off of the machine, while the device36 produces a temporary cut-off of the relay 7 to interrupt thedischarges between the electrode and the workpiece. When such aninterruption occurs, the cutoff of the voltage between the connectingposts 17 and 17a causes the electrode 3 to retract and increases therate of flow of the machining fluid. At the end of a temporary cut-offof the pulses, a high machining voltage appears again at the connectingposts 17 and 17a and the servo-mechanism 4 causes the advance of theelectrode 3 until the machining resumes under normal conditions.

FIG. 2A illustrates the over all diagram of a complete watching unit,however each of the watching units IV through IX will be described indetail with reference to FIGS. 4 through 9 respectively.

A typical watching unit comprises an adaptation circuit 200 which,through a commutator 201, can be switched either to the workpiece and tothe electrode through the lines 17 and 170, or to the measuring shunt S,through the lines 18 and 18a. This adaptation circuit transposes theinlet signal into an adequate form compatible with the other electroniccircuits which it supplies.

The signal supplied by the adaptation circuit 200 can be checked by oneor several watching circuits at an instant or during a well determinedperiod of time with respect to the application of the machining voltageor with respect to the establishment of the machining current. To thiseffect, the watching unit can encompass several multiplying circuits202, 202', 202", each fed by the output signal of the adaptation circuit200. Each multiplicator allows the passage of the signal for adetermined laps of time by means of a timer 203, consisting, forexample, of a monostable multivibrator for which the period ofinstability is triggered by a delay circuit 204 connected at will by aninverting switch 205 to one of the lines 190 or 19b. The exit signal ofthe multiplicator 202 is then transposed into a form usable by thecircuits 206, 206, 206". In this manner, we obtain at exit 207, 207',207" the representative signals of the machining conditions which aresought after.

DESCRIPTION OF THE LOGIC CIRCUIT FIG. 3 illustrates the logic part ofthe circuit 20, reference to which was made with respect to FIG. 2. Thecircuit comprises numerous gates, all of the NO -AND type. As we know,this type of gate does not transmit a signal when both entrances arereceiving a signal. As soon as one or more entrance signals are missing,the NO AND" gates are transmitting an exit signal.

The incomming signals from lines 21 and 22 are first inverted by thegates 40 and 41, to be applied to a gate 42 of which the output signalis inverted by a gate 43 prior to being applied to one of the inlets ofa gate 44 connected to lines 23 and 28.

The output of gate 44 ends, on one side to a delay circuit 45, and onthe other side to a gate 46 controlling a transistor 47 for theillumination of the pilot light 31.

The output of the delaying circuit, which imposes a 3 ms. delay to thereceiving pulses, is connected to a counting circuit 48, himselfconnected to a holding circuit consisting, in known manner, of two NO-AND" gates 49, 50 connected in series, the output of the second gatebeing connected to one of the inlets of the first gate. This holdingcircuit strikes a gate 51 followed by an inverting gate 52 controlling atransistor 53, the collector which is connected, through line 14f, tothe relay of the cut-off device 35, previously mentioned with respect toFIG. 1A, then to a feeding connecting post a. The energization of thecoil of this relay causes the opening of its contact 35a and thus thedefinitive cutoff of the machine.

The lines 23, 25 and 28, connected to the three inlets of the gate 44,are also connected to three of the four inlets of a gate 56. The fourthinlet of this gate receives the output signal of the gate 44. When allmachining conditions are satisfactory, each of the inlets of the gate 56are receiving a signal, so that the output of this gate is void of anysignal. The absence of signal at this output inhibits an impulsegenerator 57, the output of which is connected to the counter 48. Theimpulses supplied by the generator 57 are resetting the counter at zero.

The lines 24, 25 and 28 are connected to the inlets of a gate 58, theoutlet of which is connected, similarly to gate 44, to a pollutiondefect display circuit consisting of a gate and a transistor for theillumination of the pilot light 32. The gate 58 is also connected to adelay circuit 59, the delay of which is set at approximately 30 ms.

Similarly, the line 26 is connected to a gate 60 the second inlet ofwhich is connected to the line 28. The outlet signal of this gate 60 isapplied similarly to 58, on one side to a signalization circuitcomprising the pilot light 33 and on the other side to a delayingcircuit 61.

The output of the delaying circuits 45, 59 and 61 are applied three ofthe four inlets of a gate 62. The fourth inlet is fed by the output of agate 63, one entrance of which is itself connected to the output of thegate 62 to constitute a holding element assembly. The output of the gate62 is connected to a transistor 64 controlling, through the line 14e, arelay 65, the contact 66 of which is normally closed when the machiningis proceeding under satisfactory conditions. This relay 65 is part ofthe pulsator 36 which, in fact, constitutes a cutoff device. The contact66 allows the interruption of the base current supplied to thetransistor T The outlet of the gate 63 is applied to a pulse generator67, the pulses of which are striking a gate 68, the outlet of which isconnected to the inlet of the gate 63.

The lines 27, 28 and 29 are connected to the inlets of a gate 69controlling a holding circuit composed of two gates 70 and 71cooperating with a display device similar to the one previouslydescribed and controlling, eventually, the pilot light 34. The outlet ofthe gate 70 is connected to one of the inlets of the gate 71, the secondinlet of the latter receiving a signal as soon as the machiningoperation is started.

The outlet of the gate 71 is connected to an inlet of the gate 51 toallow the definitive cut-off of the machine when the line 29 is emittinga signal indicating a malfunction of the relay 6.

The functioning of the logic circuit according to FIG. 3 is illustratedby the following table, in which the ab- Satisfact. machin.

Finish 'Shortcircuit Poll'u- Are Unit line Wait Roughing tion VII, 25

VII, 26

VII, 27

VIII, 228....

Gate 44..."

Gate 58 Gate 60"...

Gate 56.

DESCRIPTION OF THE WATCHING UNITS a. Watching unit IV FIG. 4 illustratesthe watching unit IV detecting the presence of abrupt variations of themachining voltage, that is to say, of the voltage between the electrode3 and the workpiece 2, occuring during the time intervals comprisedbetween instants corresponding to the beginning of the current pulsesand the instants corresponding to their ending, exclusive of theinstants. This watching unit comprises two inlet posts which areconnected to the inlets l7 and 17a, illustrated in FIG. I. The circuitcomprises also an entrance post 19b intended to receive a signalsynchronized with the beginning of the establishment of the machiningcurrent during each voltage pulse applied between the electrode and theworkpiece. The means to generate the signal applied to the post 19b arenot described here in detail, since they are not part of the presentinvention.

The machining voltage at inlets 17 and 17a is conveyed by a resistor R acapacitor C and a diode D, to a capacitor C which will be charged to apotential relating solely to the level of the alternating component ofthe machining potential. In fact, the continuous component can not passthrough the capacitor C,. To avoid interference between the voltage ofthe capacitor C and the high frequency components which are inherent tothe application of the machine voltage between the electrode and theworkpiece as well as the abrupt voltage drop at the time of theestablishment of the discharge, a transistor T is connected toshortcircuit the high frequency component passing through the capacitorC; as long as the discharge is not effected. To this effect, the base ofthis transistor is connected to the post 19b through a gate 73constituting a signal inverting element. In this manner, the highfrequency components are not reaching the diode D and the capacitor Cexcept during the time of each discharge. The capacitor C is shunted bya discharge resistor R providing, with this capacitor, a time constantlong in relation to the duration of the discharges. The potential of thecapacitor C is applied to the inlet of a comparator 74, the second inletof which receives a reference potential obtained by a voltage divider,formed by two resistors R and' R As long as the voltage of the capacitorC is inferior to the voltage of reference, the comparator 74 supplies acontinuous signal at its output. This signal is interrupted as soon asthe voltage of the capacitor C is higher than the reference voltage. Theoutput signal of the comparator 74 is inverted by a gate 75, the outputof which is connected to the inlet of a gate 76 and to an inlet D of adelay memory 77, or flip-flop delay. The other inlet CP of thisflip-flop 77 receives the pulses exiting from the gate 73. At the exit Qof the flipflop 77, we obtain a signal corresponding to the signal whichwas applied at the inlet post D during the passage of the last positivefront of the pulse applied to the post CP. This output signal of theflip-flop 77 is applied to an inlet of a gate 78, the other inlet ofwhich receives the signal exiting from the gate 73. The output of thegate 78 is connected to an inlet of the gate 79 of which the other inletis connected to the output of the gate 76. The latter presents still asecond inlet connected to the post 19b.

As long as the machining discharges are presenting a sufficient rate ofabrupt variations, the exit Q of the flip-flop 77 supplies a continuoussignal, so that at the output of the gate 78, that is to say at oneinlet of the gate 79, we obtain, during each discharge a pulsecomprising high frequency, the spacing of these pulses beingsynchronized with the spacing of the discharges.

The other inlets of the gate 79 does not receive a signal, except whenthe two inlets of the gate 76 are receiving a signal simultaneously,that is to say during the discharge provided by the voltage at the post1% and during the signal of the gate which indicates, with a slightdelay, the presence of abrupt variations within the same discharge. Thegate 79 emits a signal during the whole duration of a discharge and theinterval between the end of this discharge and the following currentpulse. The outputsignal of the gate 79 is transmitted through line 21 tothe logic circuit 20, as shown in FIG. 2.

b. Watching unit V According to FIG. 5, this unit comprises a voltagedivider formed by the resistors R and R supplied by theelectrode-workpiece voltage appearing at the entrances 17 and 17a. Thevoltage at the posts of the resistor R is applied to a capacitor Cthrough the intermediate of a field effect transistor T Since we desireto obtain, at the posts of the capacitor C, a voltage representing thevoltage between the electrode and the workpiece for each of thesuccessive discharges, in order to measure the variations of thisvoltage during the various discharges, it is necessary that thetransistor T, be conductive only during the discharge and benon-conductive before the end of each discharge to prevent any effect onthe potential of the capacitor C due to the dissipation of the voltagebetween the electrode and the workpiece. The variations of voltage to bedetected by this watching unit are very small in relation to the voltageapplied between the electrode and the workpiece, by the relay 7.

The control of the transistor T is effected from a signal applied to aninlet post 1% which is the same as for the watching unit IV and whichreceives pulses of a duration corresponding exactly to the duration ofeach discharge. This signal is applied to an element RC forming adifferentiating circuit 80. After differentiation, this signal isinverted by a gate 81, then it is applied to a transistor T whichcontrols the biasing voltage of the base of the transistor T In sodoing, we obtain the conductive condition of the latter during eachdischarge, each period of conductivity starting slightly after thebeginning of the discharge and ending before the end of the discharge.

The voltage of the capacitor C is applied to the base of a field effecttransistor T As known, transistors of this type have an input impedancepractically infinite so that the capacitor C holds its potential,applied by the transistor T without discharge.

The transistor T controls the current flow through a resistor-R andconsequently a voltage appears at the post of this resistor,representative of the voltage between the electrode and the workpieceduring the discharges. The voltage at the posts of the resistor R can betapped by a post Va to be applied to another circuit described later.Should the gap voltage reach slightly different values for eachmachining discharge, the voltage across the resistor R varies at thesame rate, so that the alternating components of this voltage aretransmitted by a capacitor C to a converting circuit comprising a diodeD and a capacitor C The latter is therefore charged with a voltagecorresponding to the variations between the successive values of the gapvoltage. This capacitor is connected to an inlet of a comparator 82which supplies an output signal as long as the voltage of the capacitorC does not reach the level of the reference voltage applied to the otherinlet post of the comparator 82 and resulting from the passage of thecurrent through a resistor R To accommodate the circuit 20, the outputsignal of the comparator 82 is inverted, by a gate 83, to obtain at theoutput line 22 a signal (or logic state I) when the value of the gapvoltage changes slightly during 'each discharge, which indicates thatthe discharges are occuring successively at different points of thesurface to be machined.

c. Watching unit VI The purpose of this unit is to detect the pollutionlevel of the machining fluid and to emit a warning signal when thepollution reaches a level inhibitting the formation of a discharge sparkbetween the electrode and the workpiece, replaced by a current flow dueto the conductive state of the machining fluid.

FIG. 6 illustrates a pollution detecting unit sensitive to the rate ofdecrease of the voltage between the electrode and the workpiece at thetime of the establishment of the current pulses, after the applicationof the machining voltage pulse. The unit V1 is connected to the posts 17and 17a.

When abrupt variation of voltage appears between these posts, thealternating components are passing through the capacitor C and throughthe diode D when their front is of negative polarity and are charging acapacitor C when their front is of positive polarity, that is to saywhen the voltage between the electrode and the workpiece is decreasing.

Similarly to the previously described circuit, the voltage of capacitorC is compared to a reference voltage by means of a comparator 84. Theoutput of this comparator 84 is applied to a delay memory 85 whichreceives the clock pulses from the detection device 5c. In this way, theflip-flop 85 memorizes the output signal of the comparator 84 at thebeginning of each discharge. The constant RC of the capacitor Cdischarging into a resistor R is sufficiently weak to practicallydissipate any charge between the end of a pulse and the beginning of thenext one. The flip-flop 10' 85 has two outlets connected to lines 23 and24. When the unit detects the presence of pollution, the line 23 doesnot receive any signal, while line 24 does receive one. In the absenceof pollution, line 23 has a voltage and line 24 is void of signal. d.Watching unit VII This unit is intended to detect the level of thevoltage during the current impulse and memorize the related information.The diagram of this unit is illustrated in FIG. 7 and comprises avoltage divider formed by two resistors R and R connected to the inlets17 and 17a.

A second voltage divider supplies a reference voltage to the inlet of acomparator 86. This comparator 86 emits a signal when the referencevoltage is of higher value than the machining voltage, while a reverseratio of these voltages results in the absence of signal at the outputof said comparator. This output is connected, on one side, to the line27 and, on the other side, to a flip-flop 87. This flip-flop receivesthe pulses from the post 19b, in order to memorize the output signal ofthe comparator 86 at the instant corresponding to the beginning of eachdischarge. The flip-flop has two outlets connected to lines 25 and 26.The outlet 25 receives a signal when the voltage is higher, and nosignal when the voltage is lower than the reference voltage. The line26, to the contrary, indicates by a signal the fact that the voltage islower than the reference voltage.

e. Watching unit VIII This unit illustrated in FIG. 8 comprises,similarly to the one illustrated in FIG. 7, two voltage dividerssupplying, on one side, a voltage proportional to the machining voltage,present between posts 17 and 17a, and a reference voltage on the otherside. Both voltages are applied to the inlet of a comparator 88 whichprovides an output signal each time the voltage between the electrodeand the workpiece is of higher value than the reference voltage.

During the discharge between the electrode and the workpiece, themachining voltage is about 20 volts, while the voltage applied to theelectrode by the relay is much higher, in the order of volts, forexample. By appropriate selection of the voltage dividers, it is easy toobtain a signal whenever the gap voltage is lower than 30 volts, forexample.

The output signal of comparator 88 is inverted twice successively bygates 89 and 90, in order to obtain a signal impedance compatible withcircuit 20.

f. Watching unit IX This watching unit is illustrated in FIG. 9. Itsinput signal is also the gap voltage, tapped at posts 17 and 17a. Thisvoltage passes through a differentiating circuit comprising a capacitorC and a resistor R The time constant of C and R is therefore shorterthan the duration of a pulse, and this differentiating circuit providesvoltage spikes of positive polarity, respectively of negative polarity,for each positive or negative front of the machining voltage. The frontsof positive polarity are led by a resistor R to the base of a transistorT which himself monitors a second transistor T intended to shunt acapacitor C charged through a resistor R A resistor of low value Rlimits the discharge current into the transistor T as well as atransistor T connected in parallel with the transistor T but controlledby the output voltage of the differentiator, in order to becomeconductive for each negative pulse of the differentiator.

As a result, the capacitor C is charged through resistor R but isperiodically discharged by one or the other transistors T and T Thepotential of the capacitor C is applied to a unijunction transistor TWhen a defect is present in the relay and when the latter does no longerdeliver successive pulses, no voltage appears at the output of thedifferentiator, and the transistors T and T remain non-conductive. Thecharging of the capacitor C proceeds and as soon as its potentialreaches the critical level of the unijunction transistor T the latterbecomes conductive and the capacitor discharges itself into a resistor Rsupplying in so doing a pulse on line 29. This pulse is applied to thecircuit 20 and triggers, through the latter, the definitive cut-off ofthe machine, in order to prevent any damage to the electrode, to theworkpiece or to other elements of the installation.

DESCRIPTION OF AN AUTOMATIC CONTROL DEVICE FIG. 10 illustrates anautomatic control circuit of the servo-mechanism 4., controlling thedisplacement of the electrode 3. The main purpose of thisservo-mechanism is to maintain a precise distance between the electrodeand the workpiece, to obtain the optimum machining conditions.

This circuit has an inlet 17a connected to the workpiece 2, and an inletVa which is connected to the post similarly designated in the watchingunit V (FIG. 5). As previously mentioned, a voltage representative ofthe gap voltage appears at this inlet Va, during the discharge only.This voltage is continuous, but variable, and it is applied, through aresistor R to the inlet of an amplifier 91, the output of whichconstitutes the output 15 of FIG. 1 for the application of the controlsignal of the servo-mechanism 4. This output is moreover connected tothe inlet post 92 of this amplifier 91,

through a variable resistor R which allows to determine the gain of theamplifier 91.

The amplifier 91 also receives on its post 92 and through the resistorsR and R two signals relating to the time delay and the presence ofshort-circuits respectively.

The signal, which is function of the time delay, is obtained from anamplifier 93, the inlet post 94 of which is connected through a resistorR to the post 28 which constitutes the outlet post of the watching unitVIII (FIG. 8). This post 28 receives a signal each time the gap voltageis higher than, for example, 30 volts, in other words, during the wholeduration of each time delay.

The output of the amplifier 93 is connected to its inlet 94 through aresistor R in parallel with a capacitor C This feed-back circuit, on theone hand, defines the gain of the amplifier and, on the other hand,insures the integration of the input signal. Thus, a voltage is obtainedat the output of the amplifier 93, which is proportional to the rate oftime delay, in other words, to the average duration of the time delay,in relation to the machining time. From an increase of the output Signalof the amplifier 93, results an increase of the signal applied to theamplifier 91, and ultimately a control signal reducing the distancebetween the electrode and the workpiece.

The circuit of FIG. 10 further comprises an amplifier 95, the inlet ofwhich is connected to the outlet post 25 of the watching unit VII,illustrated in FIG. 7. This post 25 receives a signal, in the absence ofa short-circuit, and conversely, receives no signal as soon as ashortcircuit between the electrode and the workpiece occurs. The inputsignal is amplified and integrated by the amplifier which has, similarlyto the amplifier 93, a feed-back circuit formed by a resistor R and acapacitor C The ratio of the resistors R R R and the gain for theamplifiers 93 and 95 are affording a selective choice to obtain thedesired effect on the servomechanism, in response to the output signalof the different watching units.

FIG. 11 illustrates an automatic control device for the time interval.The function of this device is to vary the time interval between twopulses, according to the rate of unsatisfactory pulses, on the one hand,(action 1), and on the other hand, after each pulse (action 2). A highrate of unsatisfactory pulses results in an increase of the timeinterval between pulses.

This unit comprises a voltage divider formed by the two resistors R andR connected, on one side, to a set potential of -l2 volts, and on theother side, to the current inlet post connected to the outlet of thegate 43 of FIG. 3. The inlet signal is of the logic type. A level of 0volt indicates good machining pulses, while a level of +5 voltscharacterizes bad pulses.

The inlet signal acts upon two distinct circuits. The first (action 1)comprises an inverting circuit, formed by a transistor T and by aresistor R The collector of T is connected, through a resistor R to aninlet post 97 of an amplifier 98, the other inlet post being at a setpotential obtained by a voltage divider formed by the resistors R and RThe outlet post of the amplifier 98 is connected, on one side, to theinlet post 97 of a feedback circuit formed by a resistor R setting thegain of the amplifier and by a capacitor C integrating the inlet signaland, on the other side, to the base of a transistor T through a voltagedivider formed by the resistors R and R The output potential of theamplifier 98 increases its positive polarity as the rate of bad pulsesgets higher, resulting in a decrease of the emitter collector current oftransistor T The second circuit (action 2) is an inverting circuit. Theinput signal is applied to the base ofa transistor T through aresistance R The collector of this transistor is connected to theemitter of the transistor T through a voltage divider formed byresistors R and R When the pulse is good, this circuit has no effect onthe transistor T on the contrary, when the pulse is bad, the potentialof the emitter of the transistor T is decreased, so that the emittercollector current intensity also decreases.

The collector of the transistor T is connected, through line 14d, to thecapacitor C of a monostable circuit, This circuit is controlled by asignal applied to the post 1%, the duration of which corresponds to thedischarge time of the machining pulses. This signal is applied to thebase of the output transistor T of the monostable, through anintegrating circuit formed by a capacitor C and a resistor R and a diodeD which allows the passing of spikes of negative polarity only. The endof the pulses, applied to the post 190, inhibits the transistor T whichrepresents the front of the output signal which will extend until thecapacitor C is charged to a sufficiently high potential to unlock thetransistor T The duration of the output signal is therefore proportionalto the charging rate of the capacitor C which is depending on theintensity of the current supplied by the transistor T As demonstratedbefore, a high rate of bad pulses, or one bad pulse, results in adecrease of the current of the collector of the transistor T andconsequently results in a charge of the capacitor C at a decreased rate,thereby increasing the duration of the output signal of the monostable.This output signal is applied to the amplifier controlling the powerunits, setting, among other things, the time interval proportionately tothe duration of the output signal.

We obtain thereby an automatic adaptation of the average machiningcurrent by variation of the interval between the successive pulses,according to the momentary machining conditions prevailing within themachining gap.

FIG. 12 represents a block diagram of a circuit controlling the fluidinjection system. This circuit is controlled by signals provided by theoutlet 24 of the pollution control unit VI. The purpose of the fluidinjection control circuit is to regulate the flow of the machining fluidaccording to the degree of pollution of the fluid, within the machininggap, in consideration of the fact that when the machining fluid hasreached a certain level of pollution, the electrical discharge betweenthe electrode and the workpiece no longer produces a spark. It istherefore necessary, when the rate of bad pulses increases, to activatethe supply of clean machining fluid.

The circuit of FIG. 12 comprises a pollution level regulating unit. Thisunit comprises a comparator 100 and an integrating circuit formed by aresistor R and by a capacitor C The input signal, provided by the outlet24 of the pollution control unit VI, is applied, after integration, atan inlet of the comparator 100, the other inlet of this comparator beingat a set reference potential. We obtain thereby, at the exit of thecomparator, a logic signal relating to the pollution level. This signalis applied to a monostable 101, the output signal of which is of aduration determined by its RC circuit. The signal is then amplified andapplied to the coil 102 of an electrovalve 103 which regulates the flowof the dielectric fluid 104.

When the pollution level of the fluid is too high, the regulatingcircuit produces a logic signal controlling the monostable 101. Thelatter produces a pulse of a determined duration, which is amplified tocontrol the opening of the electro-valve 103 for a time duration equalto the duration of the pulse, providing thereby replacement of thedielectric fluid 104 within the machining gap.

FIG. 13 illustrates the ET, circuit of FIG. 1A. This circuit comprisestwo transistors T and T the collectors of which are connected, each, onone side to the post of positive polarity of the power supply, through aresistor, and on the other side, to the base ofa transistor T by a diodeD and D The base of the transistor T is connected, by the line 14b, tothe outlet of the gate 44 of the diagram of FIG. 3. The base of thetransistor T is connected to the outlet of the pulsator 36 of FIG. 1A.

When the machining conditions are satisfactory, the outlet of the gate24 supplies a 1 signal. The outlet of the pulsator 36 also supplies a 1signal when the transistor T of the relay 7 is conductive, that isduring the application of a pulse to the electrode 3. When the bases ofthe two transistors T and T are submitted to a positive signal, thesetransistors are conductive, so that the base of transistor T issubstantially at the same potential as the emitter of this transistor.The latter is therefore non-conductive, and the potential of positivepolarity is applied to the outlet 55 through the resistor R As soon asone or the other of the transistors T and T does not receive a signal onits base, it becomes non-conductive and its collector assumes thepotential of the power supply of positive polarity. This potential isthen applied through one of the diodes D or D, to the base of thetransistor T which becomes conductive, the collector of which falls to apotential approximating 0.

When the transistor T is conductive and when at the same time the outputsignal of the gate 44 corresponds to satisfactory machining conditions,the outlet 55 receives a signal which renders the transistor Tconductive. Eventually, a plurality of transistors in parallel canprovide an optimum instantaneous machining current.

FIG. 14 represents the diagram of the ET gate of FIG. 1A. This gate hasan inlet connected to line 14a, which moreover receives the signal ofline 28 directly (FIGS. 2 and 8). This line is characterized by theabsence of signal when the control unit VIII detects a delay between theapplication of the machining voltage and the establishment of thedischarge, or, conversely, remains at a 0 potential.

The purpose of the signal of the line 14a is to charge a capacitor Cthrough a resistor R In the event of machining without waiting delay,this capacitor allows the application of a potential of positivepolarity to a differential amplifier 130, the output of which provides a0 signal. When a sufficient rate of waiting time is present, thecapacitor C discharges itself and when its potential falls below thereference potential provided by a divider, formed by the resistors R andR the output of the differential amplifier provides a l signal. Thissignal is applied to a transistor T when another transistor T is in aconductive state. The base of transistor T is connected to the pulsator36.

The transistors T and T are controlling, in a manner similar to the oneillustrated by the diagram of FIG. 13, a transistor T the collector ofwhich, by its potential, commands the base of the transistor T (FIG. 1A)which controls the application of high voltage to the electrode tofacilitate the establishment of the current discharge. The outlet of thegate ET supplies a signal controlling the application of the highvoltage solely during the period in which the transistor T, isconductive and during which the watching unit VIII indicates a waitingdelay.

FIG. 15 illustrates a circuit allowing a decrease of the dischargeduration in the event of machining presenting a too high rate of arcing.This circuit receives at its input the signal provided by the output ofthe gate 43 of FIG. 3. This signal acts on a transistor T through theintermediary of two inverting gates 131 ,and 132. This transistor Tcontrols a transistor T which becomes conductive, non-conductiverespectively, at the same time as the transistor T The transistor Tallows the connecting of a resistor R in parallel with the resistor R toincrease the charging current of a capacitor C of the monostable 5a.

Should the machining be unsatisfactory, due to the absence of highfrequency or due to the absence of variation of the tension triggeringthe spark between the electrode and the workpiece, the gate 43 (FIG. 3)will supply at its exit a l signal, which will render the transistor Tconductive as well as the transistor T The charging current flowingthrough line 14c increases then and reduces the time duration of theinstability of the monostable multivibrator 5a, and consequently theduration of each pulse.

It is well understood that the preceding description refers to oneexample of execution of the circuits, of the process and installation,object of the invention, and that similar results could be obtained bythe application of other circuits.

I claim:

1. A machining process by electro-erosion according to which asuccession of voltage pulses are applied within a machining gapcomprised between an electrode-part to be machined and an electrode-toolintended to trigger the erosive discharges through a machining fluidfilling the gap, the discharges being sustained by controlled currentpulses, and in which at least one of the following machining parametersis controlled automatically:

first, the characteristic value of said electric voltage and/or currentpulses; second, the physical or chemical condition of the machiningfluid filling the said gap; and

third, the spacing of said electrodes; by means of electric signalsobtained from measurements of the voltage between the electrodes and/orthe current flowing through the latter and/or a combination of both ofsaid signals, said process comprising detecting the decrease of saidvoltage during the establishment of the current pulses when at a ratewhich is inferior to that of a predetermined value, and acting upon atleast one of the machining parameters, in response to an electric signalresulting from the presence of the decrease of the voltage, when at arate which is inferior to that of the said predetermined value.

CMS UNITED STATES PATENT OFFIQE CETIFICATE @F (IQRRECIIQN Patent No. 3,739,137 Dated June 12, 1973 Inv 1 Georges -Andre Mar endaz It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

IN FOREIGN APPLICATION PRIORITY DATA:

0Q...IQQCOUCQUOUB44OZ/71" IN THE SPECIFICATION:

Column 2., line 24, change "exit" to --output-- line 39, change "exit"to --output-- line 49, change "exit" to --output-- line 51, change"inlet" to --input-- line 55, change "inlet" to --input-- line 56,change "position" to --state-- line 59, change "entrance" to --inputline 61, after "between" insert --the inputs-- line 62, after "172."insert --of the control device 13-- FORM POJOSO (169) USCOMM-DC60376-P69 t U.$. GOVERNMENT PRINTING OFFICE 1 I959 -365'334 Patent No.3, 739,137

Page Two Column 3,

Column 5',

line 47, change "inlets" to --inputs-- line 51, change "outlets" to--outputs-- line 52, change "outlet" to --output-- line 55, change"outlet" to --output-- line 58, change "outlet" to --output-- line 61,change "outlet" to --output-- line 8, change "outlets" to --outputs--line 14, change "connecting posts" to --1ines-- line 18, change"connecting posts" to --lines-- line 26, after "unit" insert a commafollowed by --as illustrated at FIG. 2A-- line 43, after the commainsert 203', 2.03", each-- line 47, change "exit" to --output-- line 50,change "exit" to --output-- lines 57 8: 58, cancel""NO -AND"" and insertthereinstead line 60, change "entrance" to --input-- line 61, change "NO-AND" t0 "NAND"-- change "exit" to --output-- line 64, change "gates" to--inverters-- line 65, change "gate" to --inverter-- line 66, change"inlets' to --inputs-- Patent No. 3, 739,137 Page Three Column 6, line3, change "receiving" to --received-- line 4, change "himself" to--itself-- line 5, change "NO -AND" to --"NAND"-- line 7, change"inlets" to inputs lines 9 8: l0, after "collector insert --of-- line13, after "coil" insert "54-- line 14, change "35a" to --55a-- line 16,change "inlets" to --inputs-- line 18, change "inlets" to --inputs--change "inlet" to --input-- line 20, change "inlets" to --inputs-- line27, change "inlets" to --inputs-- line 35, change "inlet" to --input--line 36, after "to" insert --that of gate-- line 41, after "applied"insert --t?o-=- change "inlets" to -inputs-- line 42, change "inlet" to--input-- change "entrance" to --input-- line 52, change "outlet" to--output-- line 54, change "outlet" to --output-- change "inlet" to--input-- line 55, change "inlets" to --inputs-=-=

1. A machining process by electro-erosion according to which asuccession of voltage pulses are applied within a machining gapcomprised between an electrode-part to be machined and an electrode-toolintended to trigger the erosive discharges through a machining fluidfilling the gap, the discharges being sustained by controlled currentpulses, and in which at least one of the following machining parametersis controlled automatically: first, the characteristic value of saidelectric voltage and/or current pulses; second, the physical or chemicalcondition of the machining fluid filling the said gap; and third, Thespacing of said electrodes; by means of electric signals obtained frommeasurements of the voltage between the electrodes and/or the currentflowing through the latter and/or a combination of both of said signals,said process comprising detecting the decrease of said voltage, duringthe establishment of the current pulses when at a rate which is inferiorto that of a predetermined value, and acting upon at least one of themachining parameters in response to an electric signal resulting fromthe presence of the decrease of the voltage when at a rate which isinferior to that of said predetermined value.
 2. A process according toclaim 1, wherein means are provided for the detection of the decrease ofthe voltage, the rate of which is substantially superior to that of thesaid pre-established value, during the establishment of the currentpulses and for obtaining said signal in response to the presence of thedecrease of the voltage, the rate of which is sensibly superior to thatof the predetermined value.
 3. A process according to claim 1, wherein apredetermined value is given to said electric signal when, during theestablishment of the current pulses, a voltage decrease is detected, therate of which is inferior to that of a predetermined value.
 4. A processaccording to claim 1, wherein said electric signal is given, atsuccessive instants repeated at a rhythm identical to that of thecurrent pulses, a value, function of the rate of decrease of the voltageat the moments of establishment of the current pulses included betweenthese instants.
 5. A process according to claim 4, wherein said electricsignal is given, at said instants, a predetermined value, when the rateof decrease of the voltage is inferior to that of a predetermined value,and another predetermined value, when this rate of decrease is superiorto that of a predetermined value.
 6. A process according to claim 1,wherein action, on at least one of the machining parameters is provided,by means of a combination of said signal, obtained in response to thepresence of the voltage decrease for which the rate of decrease isinferior to that of a predetermined value, with at least anotherelectric signal elaborated by detecting the abrupt variations of saidvoltage occuring during the time intervals included between instantscorresponding to the beginning of the current pulses and instantscorresponding to their ending, exclusive of these instants, this otherelectric signal being obtained in response to the presence, respectivelyto the absence of these abrupt variations of voltage during these timeintervals.
 7. A process according to claim 1, wherein action is providedon at least one of the machining parameters, by means of a combinationof said signal, obtained in response to the presence of a decrease ofthe voltage, which rate of decrease is inferior to that of apredetermined value, with at least another electric signal, elaboratedby effecting repeated measurements of the average level of the voltagebetween the electrodes during the time intervals included between theinstants corresponding to the beginning of the current pulses and theinstants corresponding to their ending, by memorizing the result ofthese measurements and by comparison between them, the results of thesemeasurements from one current pulse to another, the said signal beingelaborated from the differences of these results.
 8. A process accordingto claim 1, wherein action is provided on at least one of the machiningparameters, by means of a combination of said signal, obtained inresponse to the presence of the decrease of the voltage, the rate ofwhich decrease is inferior to that of a predetermined value, with atleast one other electric signal elaborated, in known manner, from thecomparison of a reference value, with the result of repeatedmeasurements of the average level of the voltage between the electrodes,effected during the time intervals included between the instantscorresponding to the bEginning of the current pulses and the instantscorresponding to their ending.
 9. A process according to claim 1,wherein action is provided on at least one of the machining parameters,by means of a combination of said signal, obtained in response to thepresence of the decrease of the voltage, which rate of decrease isinferior to that of a predetermined value, with at least one otherelectric signal which is elaborated in a known manner, from the repeatedmeasurements of the voltage between the electrodes effected during thetime intervals included between the instants corresponding to thebeginning of the tension pulses and the instants corresponding to thebeginning of the current pulses.
 10. A process according to claim 1,wherein the chemical or physical conditions of the machining fluidfilling the machining space can be altered in response to said electricsignal.
 11. A process according to claim 10, wherein the rate of renewalof the machining fluid within the machining space can be altered inresponse to said electric signal.
 12. An installation for working outthe process according to claim 1, wherein first means are comprised,sensitive to the rate of the voltage variations between theelectrode-part and the electrode-tool, of an amplitude superior to thatof a predetermined value and second means, operatively related to thefirst means, conceived and disposed in a manner permitting the deliveryof a signal intended to act upon at least one of the machiningparameters, this signal being obtained in response to the rate of speedof said variations.
 13. An installation according to claim 12, whereinthe first and second means are conceived and disposed in a mannerallowing the second means to assume two distinct electrical conditions,contingent upon the rate of speed of said variations being superior orinferior to that of a predetermined value.